And the other possibility, already mentioned, with the same result: a mounted camera hits something, stops head and helmet rotating but the brain continues to move inside the skull.
Not exclusively with an attached camera or the like. It's what happens if you smack your crash helmet on anything. It s also the reason why Professional Boxers are required to have CT scans one or twice a year.
Heavy punches delivered to the head, especially as a 'hook', tend to rotate your skull while your brain stands still due to inertia. Then your bran begins to catch up just as your skull starts coming back. This tends to tear the nerve bundle joining your right and left hemispheres.
Never seen the point of boxing, even if I had never seen boxers CT scan results.
Roger